Process of treating pyro smokeless powder



Patented Dec. 19,1922.

,UNITED STATES 1,439,656 PATENT OFFICE.

RICHARD G. WOODBRID GE, OF WILMINGTON, DELAWARE, ASSIGNOR ,TO E. I. DUPON'I' DE NEMOURS & COMPANY, OF

WARE.

WILMINGTON, DELAWARE, A CORPORATION OF DELA- PROGESS OF TREATING 'PYROSMOKELESS POWDER.

No Drawing.

To all whom it may concern:

Be it known that I, RICHARD G. WOOD- BRIDGE, a citizen of the,UnitedStates, and

a resident of Wilmington, inthe' county of New Castle and State ofDelaware, have invented-a certain new and useful Process of TreatingPyro Smokeless Powder, of which the following is a specification. I,

This invention relates to the treatment of pyro smokeless powder for thepurpose of reducing the viscosity-characteristic thereof, thereby makingpracticable the use of the powder as an ingredient of coatingcompositions.

By pyro smokeless powder, or pyro powder, is meant that grade ofsmokeless powder made from nitrocellulose almost completely soluble in amixture of two parts by volumev of ether to one part of ethyl alcohol.and having a nitrogen content of about 12.60%. When the World Warterminated in the year 1918, there existed large surplus stocks of thispyro powder originally containing about 0.5% of diphenylamine.

Some of this powder is not suitable for use in arts other than theexplosive art because the powder grains are diflicultly soluble 1n theusual pyroxylin solvents on account of their relatlvely large size, butmore especially on account of the powder grains giving very viscoussolutions. For some uses, the presence of the diphenylamlne is obiectionable because the diphenylamine reacts with the decompositionproducts of the powder forming colored nitroso and nitro derlvatives andmixed IHtIOSO IHtI'Q derivatlves, besides other colored derlvatives, the

' identity. of which has not been fully established. Thus, pyroxylinsolutions containing diphenylamine are unsuitable except for use in verydark colored products, although diphenylamine itself is an excellentstabilizer and, were it not for its hlghly colored derivatives, might bea .very desirable ingredient of pyroxylin solutions. Another objectionis that the presence of diphenylamine in pyroxylin solutions causes areduc- :tion in their viscosities to take placeat a faster rate thanthat when diphenylamine 1s absent. For many purposes th1s 1s. notobje'ctionable, but it may' be very ob]ect1onable when considerable timeelapses between the preparation and the use of' the pyroxylinsolution. I

Application filed March 13, 1922. Serial No. 543,475.

I have discoveredthat by a prolonged heatlng of pyro powder whileimmersed in an organic liquid which is substantially a non-solvent forthe powder, such as ethyl alcohol, toluene, etc., the powder may be sochanged as to impart to its solutions a much lower viscosity than thatof corresponding solutions made from untreated powder. My new processcomprises immersmg the powder grains in a liquid of the kindabove-described and heating the mass, preferably at, or near, theboiling point of said diphenylamine, and have also considerable, if notexcellent, solvent action for the nitrosoand nitro derivatives ofdiphenylamine.

I do not.confine myself to the use'of a single liquid such as ethylalcohol or benzene, as it is obvious that I can use various mixtures ofliquids. For example, a mixture of ethyl alcohol and benzene in equalparts may be used, for although this mixture has a very high solv'ehtaction on nitrocellulose of about 11.0% nitrogen, the solvent actionmaterially decreases as the nitro gen increases, and on pyro powderthere, is no solvent action but only slight swelling of the powdergrains. Instead ofbenzene, toluene or xylene or mixtures thereof may beused with'th'e ethvl alcohol or with other be illustrated by thenon-solvents for nvro powder, but,

by immersing it in denatured ethyl alcohol containing gal. benzene to100 gals. of ethyl alcohol, the denatured alcohol being boiled in asuitable still provided with a condenser for condensing the alcohol andreturning same to the still for reuse. The viscosity of the powder wasoriginally 250 seconds in a solvent mixture composed of benzene 50,ethyl alcohol 20, and ethyl acetate 30, parts at a temperature of 28 C.by the so-called steel ball method, this time being that required by a1} steel ball to fall through 10 of a solution containing 16 oz. of thepowder to 1 gal. of the solvent mixture given above. After heating thepowder in boiling ethyl alcohol for about 75 hours, usingsufiicientalcohol to keep the powder always covered, the viscosity ofthe powder was reduced to 20 secs. and the content of thediphenylamine,- both converted and unconverted, remaining in the powderwas less than 0.02%, a practically negligible amount.

During the boiling treatment, the alcohol may be changed several timesif extraction of the diphenylamine and its derivatives to a minimumquantity is desired. By unconverted diphenylamine, I mean diphenylamineplus the nitroso-diphenylamine, the latter having been shown byinvestigators to be almost the equivalent of diphen lamine in itsstabilizing action on powder. y converted diphenylamine, I refer to thenitro derivatives of diphenylamine.

When" the viscosity-characteristic of the pyro powder is originally low,a shorter time of treatment in boiling ethyl alcohol is requ red inorder to reduce the viscosity to a point where the powder is suitablefor use 1n the preparation of pyroxylin solutions. F or example, a 30hour boiling treatment in ethyl alcohol sufficed to reduce theviscosity-characteristic of a sample of pyro powder to such an extentthat. the viscosity of its solution was reduced from 85 to 20 secs., thecontent of converted and unconverted diphenylamine remaining in thepowder being reduced to less than 0.02%.

I have also discovered that different liquids do not have the sameeffect in regard to reduction in viscosity, even though they may be usedat the same temperature; and that different liquids extract more or lessof the diphenylamine and its derivatives. For example, a 30 hr. boilingtreatment of the above pyro powder in benzene reduced the viscosity toonly 76 secs. while the content of converted and unconverteddiphenylamine remaining in the powder was 0.32%. On the other hand, byboiling the same pyro powder i'ntoluene of the commercial grade with aboiling point of approximately 111 Q, the viscosity was more rapidlyreduced than when boiled in benzene; thus 24 hoursofboiling with toluenesufficed to reduce the viscosity of the particular sample of pyro powderfrom 85 secs. to 17 secs., the content of converted and unconverteddiphenylamine remaining in the powder being 0.41%. After 40 hoursboiling with toluene, the diphenylamine content was 0.35% and theviscosity of the solution was'5 seconds.

While it is impossible to remove the last traces of nitro derivatives ofdiphenylamine, the amount remaining in the powder is so small as topermit the powder to be used in the preparation of pyroxylin solutionswhere a light color is an important feature. Where the presence of thediphenylamine in the treated powder is not objectionable, I may heattreat the pyro powder in toluene or other liquid or mixtures of liquidswhich, while effecting only partial extraction of the diphenylamine,will reducethe viscosity of the powder in an economical manner.

In certain cases the reduction of the diphenylamine content is the mostimportant feature of the process, especially where the pyro powderavailable already possess such a low viscosity characteristic as torequire but a slight further reduction. In bringing about this reductionin diphenylamine content, the difference in the effectiveness of analcohol, such as ethyl alcohol, on the one hand, and of a benzenoidhydrocarbon on the other, is remarkconditions of time andtemperaturewill remove no more than about 25% of the di 'phenylamine initiallypresent.

- This greater effectiveness of the alcohol in removing diphenylamine isnot due to a greater solvent power possessed by the alcohol fordiphenylamine, since the latter is more than twice as soluble in benzeneand toluene as it is in ethyl alcohol.

While I prefer, in practicing the process, to maintain the particularliquid employed at or below its boiling point because of the simplicityof apparatus required, it. is sometimes expedient to heat the pyro pow-'der in the liquid at temperatures above its normal boiling point, forexample between 75 and 135 C., by the use of an autoclave.

In any event, in the heat treatment of the powder, I prefer to usetemperatures at which objectionable decomposition of the to use theliquids previously mentioned at or characteristic of pyro powdercontaining near their boiling points-ethyl alcohol and benzene, forexample, at a temperature of approximately180 C., toluene at atemperature of about 111 C., and xylene at about 135 C. While I prefernot. to exceed a temperature of 135 C., in some cases where the powderrequires relatively little heat treatment to give it the desiredviscosity-charac terist c, I may give the powder a very short heattreatment at a temperature above 135 (3., but in all events avoidingobjectionable decomposition of the powder.

\Vhen the powder grains are large in size, for example, more than 1 inlength, I pret'er to grind or crack the powder to smaller size insuitable grinding apparatus'sothat smaller sized grains will beavailable for the heat treating process. This facilitates the extractionof the diphenylamine and its derivatives from the powder, besidesfacilitating the solution of the powder after the heat treatment iscompleted. Even when the powder grains are not large, the powder maybefirst ground to shorten the time required for extraction, but when theoriginal grains are quite small, the "decrease in extraction timeresulting from preliminarily grinding the powder may be insuflicient tojustify the .added trouble and expense of such grinding. Instead ofgrinding the powder under water, I preferablygrind the powder underethyl alcohol and either heat the powder in boiling ethyl alcohol, ordrain off the alcohol and heat the powder in toluene orjin anotherliquid or mixtures of liquids of the kind above-described.

I claim:

1. The process of reducing the viscositydiphenylamine which comprisesheating the powder, immersed in an organic liquid in which the powder issubstantially insoluble,

" at a temperature below 150 C.

2. The process of concurrently reducing the riscosity-characteristic andthe diphenylamine content of pyro powder, which comprises heating saidpowder at a temperature below 150 C. while it is immersed in a liquidwhich is a solvent for the diphenylamine but a non-solvent for theremainder of the powder.

The process of reducing the viscositydipheuylamine which comprisesheating the powder at a temperature between about 60 and 135 C. incontact with an organic liquid in which said powder is substantiallyinsoluble, until the desired change in the-viscositycharacteristic ofthe powder has occurred.

4. The process of concurrentlyreducing the viscosity-characteristic andthe diphenylamine content of pyro powder, which comprises heating saidpowder immersedin ethyl alcohol at atemperature between about 7:") and135 C. until the desired change in the viscosity-characteristic of thepowder has occurred.

5. The process of rendering pyro powder containing diphenylaminesuitable for use in light colored coating compositions, which comprisestreating said powder with an alcohol until the desired reduction in thediphenylamine content has occurred.

6. The process of renderingpyro powder containing diphenylamine suitablefor use in light colored coating compositions, which comprises treatingsaid powder with ethyl alcohol until the desired reduction in thediphenylamine content has occurred.

v 7. The process of rendering pyro powder containing diphenylaminesuitable for use in light colored coating compositions, which comprisesheating said powder with an alcohol ata temperature below 150 C. untilthe desired reduction in the diphenylamine content has occurred.

In testimony whereof I afiix my signature.

. RICHARD G. WOODB'RIDGE.

characteristic of pyro powder containing.

